1. Field of the Invention
The present invention relates to a multilayer ceramic circuit board, and more particularly, it relates to a multilayer ceramic circuit component which includes at least two types of ceramic portions having different electric characteristics.
2. Description of the Background Art
FIG. 12 shows an example of a conventional multilayer ceramic circuit board. This multilayer ceramic circuit board 1 is formed by superposing a dielectric ceramic portion 2 and a magnetic ceramic portion 3 and integrating the portions 2 and 3 with each other. The dielectric ceramic portion 2 has capacitor 5 formed in its interior. The capacitor 5 is formed by a plurality of electrodes 4 arranged in layers. On the other hand, the magnetic ceramic portion 3 has an inductor 7 which is formed by a conductor 6 having a helical structure. Further, a thick film resistor 8 is provided in the interior of the dielectric ceramic portion 2.
The dielectric ceramic portion 2 contains a ceramic material of a Pb composite perovskite system or a BaTiO.sub.3 system, for example, while the magnetic ceramic portion 3 contains a magnetic ceramic material of an Mn--Zn ferrite system or an Ni--Zn ferrite system, for example. The thick film resistor 8 contains a resistive material of a ruthenium system or a lanthanum system, for example.
Such a multilayer ceramic circuit board 1 is manufactured by stacking a plurality of dielectric green sheets and a plurality of magnetic green sheets respectively, heating the laminates under pressure, and then integrally firing the same. Conductive paste for defining the electrodes 4 and resistive paste for forming the thick film resistor 8 are previously applied to some of the dielectric green sheets. On the other hand, conductive paste for defining the conductor 6 is previously applied to some of the magnetic green sheets.
In the integral firing for obtaining the aforementioned multilayer ceramic circuit board t, however, it is necessary to match shrinkage factors of the different materials with each other in firing as well as to suppress mutual diffusion of components between the different materials. Therefore, the aforementioned dielectric and magnetic materials cannot be directly applied to the dielectric and magnetic ceramic portions 2 and 3 and proper additives are generally added to such materials. When the dielectric ceramic portion 2 contains a BaTiO.sub.3 dielectric ceramic material and the magnetic ceramic portion 3 contains an Ni--Zn ferrite magnetic material, for example, glass is employed for the former and CuO is employed for the latter as additives.
However, the dielectric and magnetic materials containing such additives are inferior in electric characteristics such as dielectric constants, Q values and permeabilities to those containing no additives, and hence characteristics of the capacitor 5 and the inductor 7 are disadvantageously deteriorated.
Further, the materials which are rendered capable of integral firing in the aforementioned manner are so sensitive to firing conditions that the capacitor 5 and the inductor 7 are deficient in stability of characteristics, leading to an inferior production yield of the multilayer ceramic circuit board 1 obtained by integral firing. In relation to this problem, the respective ones of the capacitor 5 and the inductor 7 as well as the thick film resistor 8 may be trimmed to be provided with desired characteristic values. In the example shown in FIG. 12, however, it may be almost impossible to trim an electric element, such as the thick film resistor 8, because the film resistor is located deeply in the interior of the multilayer ceramic circuit board 1.
The problem caused in the aforementioned multilayer ceramic circuit board 1 may also take place in another multilayer ceramic circuit board which includes at least two types of ceramic portions having different electric characteristics. For example, a problem substantially similar to the above is caused when a multilayer ceramic circuit board including a ceramic portion having a relatively low dielectric constant and that having a relatively high dielectric constant is obtained by integral firing. Dielectric members having low and high dielectric constants are thus integrated with each other since a dielectric member having a low dielectric constant exhibits an excellent temperature characteristic although the as-obtained electrostatic capacitance is small while a dielectric member having a high dielectric constant can obtain high electrostatic capacitance although its temperature characteristic is inferior in general and it may be preferable to utilize such advantages of these members in a single multilayer ceramic circuit board. The dielectric member having a low dielectric constant is prepared from a dielectric ceramic material of an alumina-glass system of a BaO--Al.sub.2 O.sub.3 --SiO.sub.2 system, for example. The dielectric member having a high dielectric constant is prepared from the aforementioned dielectric ceramic material of a BaTiO.sub.3 system or a Pb composite perovskite system, for example.